This relates to graphics processing and, particularly, to motion blur and depth of field rendering.
Motion blur is the effect where moving objects appear blurred when captured with long camera exposure times. Depth of field is the effect that a larger aperture has a shorter focus range, and objects out of focus appear blurred.
One of the most important culling tests is backface culling. Backface culling eliminates rasterization processing of objects that face away from the camera. A rendering primitive can be backface culled if its face normal makes an angle of more than 90 degrees with the camera view vector. By culling these rendering primitives, unnecessary processing may be reduced.
When rendering motion blur and depth of field, an excessive amount of inside or intersection tests can be generated, and therefore, accurate backface culling tests are needed also for these contexts. For moving triangles, where each vertex moves along a line in three dimensions, a moving triangle is commonly assumed to be backfacing over the entire time interval if the triangle is backfacing at the start of the motion and at the end.